1. Field of the Invention
The present invention is directed to catheter electrodes for the relief of pain. More particularly, the present invention is directed to a catheter for electrical stimulation of the epidural space and administration of local anesthetics.
2. Description of Related Art
Electrical stimulation of the spinal column through electrodes implanted in the epidural spaces has been found useful in controlling pain. The use of injected anesthetics or narcotics has been found useful in the temporary relief of pain. In some instances, the local anesthetic or the narcotic is administered into the epidural spaces along the spinal column. These and other techniques are used to control intra-operative pain, post-operative pain, and chronic pain states. Such techniques as currently practiced, however, leave many patients without satisfactory pain relief.
This is a result of the characteristics of the modalities for pain control and of the nerves that carry pain impulses. The nerve fibers carrying pain impulses to the spinal cord are classified into three major groups according to their speeds of conduction. Type A nerve fibers carry pain impulses at the rate of about thirty to one hundred-twenty meters per second. Type B nerve fibers carry pain impulses at the rate of about five to fifteen meters per second. Type C nerves carry pain impulses most slowly of all, about 0.1 to two meters per second. These fibers all relay impulses through an area in the spinal cord called the substantial gelatinosa. From this site, the nerve fibers are projected to the brain. The three primary modalities for pain control and their primary disadvantages are as follows.
First, local anesthetics may be injected. Local anesthetics act by blocking the transmission of pain impulses in types A, B and C nerve fibers. Local anesthetics typically, however, relieve pain only a relatively short time and if large amounts are injected into the epidural spaces to achieve longer term pain relief, the local anesthetic is absorbed into the blood stream and leads to local anesthetic toxicity. Consequently, typical anesthetics must be administered every hour or two.
Second, narcotics, such as morphine sulfate, or methadone, may be injected into the epidural spaces. Narcotics act by modulating the impulse transmission at the substantial gelatinosa. Narcotics are, however, extremely dangerous and may well spread upwards into the brain and lead to the arrest of breathing, and to death. Narcotics typically bring pain relief within from about twelve minutes to about twenty-five minutes and provide continuous pain relief for six to about eighteen hours, depending on the particular narcotic used and the type of pain being treated. Because narcotics may be extremely addictive, physicians generally prefer to use non-narcotic pain relievers whenever possible.
Third, an optimal amount of electrical stimulation of the spinal cord through the epidural spaces is used to relieve pain, but acts almost exclusively on the pain impulse traffic along the type C fibers in the spinal nerves, leading to only a 50%-60% reduction in pain. This well-established modality is used in the treatment of pain from chronic inflammation, and chronic pain from cancer, old injuries, nerve injuries, and so forth and can be permanently implanted, complete with its own subcutaneous power supply, for example Trojan et al U.S. Pat. No. 4,549,556. Although it is useful for many patients, electrical epidural nerve stimulation does not lead to full, or even satisfactory pain relief in many other patients.
In addition, in the case of an injected pain-relieving agent, whether local anesthetics or narcotics, the drugs quickly relieve pain but their pain killing ability dissipates over time due to absorption of the pain reliever by the body, which metabolizes the agent. Thus, the pain-relieving agent must be administered periodically and frequently. Typically, either local anesthetics or narcotics are administered every two to six hours (although some narcotics may provide pain relief for up to about eighteen hours in some cases). This regimen requires the regular attendance by a trained medical worker who must monitor the patient's pain, the dosage and timing of the injections, and then repeatedly administer the drug. This process is labor intensive. Even more importantly, it results in wide undulations in the level of pain experienced by the patient. When the anesthetic or narcotic is first administered, nearly all the pain vanishes. With the passage of time, however, the pain returns before the next dose is given. If doses are spaced closely enough to prevent the recurrence of pain, overdosing the patient is quite likely.
During operations, anesthesia must be administered through a different method than is used to control post-operative pain. In some cases, even in a hospital, overdoses of narcotics lead to the death of patients.
Thus, it is clear that the prior art of pain relief includes some significant disadvantages.
Therefore, a need exists for a device and a method that achieve effective full-time satisfactory relief from serious pain; that reduce the likelihood of an overdose of an anesthetic or narcotic; and permit application of a uniform dosage across time; and that permits the physician to establish anesthesia for surgery as well as to control post-operative pain.